Answer:
A sea sponge 760 million years old
Explanation:
It's unclear exactly how long sea sponges have been around, but they are at least old enough to be the longest-existing creatures on Earth, outside the realm of microorganisms (like bactery). The oldest evidence of a sea sponge found was a fossil discovered just last year in a 760-million-year-old rock. This beat the previous record for oldest sponge fossil, a 635-milloon-year-old sponge discovered in 2009. There may be still older fossils yet to find. But finding an older species is unlikely,as these simple organisms appear to be the progenitors of much more complicated life, including the first multicellular animals.
